The present invention relates generally to a motor construction, and more particularly to a motor construction having a motor shaft and an output shaft which can be selectively coupled with the motor shaft to be driven by the same, and can be braked.
It is known from the prior art to provide motor constructions of this type, for instance from U.S. Pat. No. 3,581,855 and from German Pat. No. 2,155,423. This type of motor construction has the advantage that the friction surfaces of the coupling plate and of the braking plate which are required can be relatively large in their dimensions, and therefore be effective, whereas the axial space required for the overall construction is relatively small, which is of course desirable.
An additional advantage of these constructions is the fact that short magnetic paths are obtained and this, in conjunction with the small airgaps required, assures that a rapidly responding magnetic system is obtained which, nevertheless, requires only a relatively small amount of electric energy. Constructions of this type are characterized by the fact that relatively short mechanical dead time exists, which is important in order to obtain a rapid accommodation of the regulating value in motors whose rotational speed is regulated. Moreover, the small regulating time required in these constructions makes possible a precise positioning.
However, for all their advantages the prior-art constructions are still possessed of certain disadvantages which must be overcome. In motor constructions of this type heat is developed not only by operation of the electromagnets, but much heat is in aaddition produced by friction since the rotational speed of the motor is controlled via the slip between the motor flywheel and the coupling plate, by intermittent operation of the coupling and the brake, or by simultaneous operation of the coupling and the brake in mutually opposite sense, that is energizaation of the brake and deenergization of the coupling, or vice versa. In addition, when the output shaft is braked further high heat values develop for at least brief periods of time, because the entire kinetic energy in the system becomes converted into heat. It is quite evident that the development of so much heat is undesirable and should be suppressed to the extent possible, especially since the friction members of the coupling plate and of the braking plate are in effect the only wear parts of the system and since their degree of wear is a function of the heat which acts upon them, so that a reduction of the heat will result in an increase of the lifetime of these components.